Process for forming schottky rectifier with PtNi silicide schottky barrier

ABSTRACT

A process for forming a Schottky barrier to silicon to a barrier height selected at a value between 640 meV and 840 meV employs the deposition of a platinum or nickel film atop the silicon surface followed by the deposition of the other of a platinum or nickel film atop the first film. The two films are then exposed to anneal steps at suitable temperatures to cause their interdiffusion and a ultimate formation of Ni 2 Si and Pt 2 Si contacts to the silicon surface. The final silicide has a barrier height between that of the Pt and Ni, and will depend on the initial thicknesses of the Pt and Ni films and annealing temperature and time. Oxygen is injected into the system to form an SiO 2  passivation layer to improve the self aligned process.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/779,836, filed Mar. 7, 2006, the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to semiconductor devices and more specificallyrelates to a novel process for the manufacture of a PtNi Silicidebarrier Schottky device.

BACKGROUND OF THE INVENTION

Schottky devices are known which use a PtNi Silicide Schottky barrier. Aprocess for the formation of such barriers in which the barrier heightis settable in the range of about 640 meV to about 840 meV would be verydesirable.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the invention, a novel process is provided in whichthe barrier is formed by a process sequence in which platinum and nickellayers of selected thickness (having Schottky barrier heights of 640 meVand 840 meV respectively) are sequentially deposited on a siliconsubstrate followed by annealing process at increasing temperatures toactivate the interdiffusion process between the barrier metals and thesilicon substrate to form a desired silicide Schottky barrier height.The final silicide will have a barrier height between that of theplatinum and the nickel.

Thus, the two layers or films of platinum and nickel respectively aresequentially deposited, as by sputtering or the like from two differentmonolithic targets in the same chamber. In this way, one can define thesilicide stoichiometry and the Schottky barrier height by varying theinitial film thicknesses and the annealing temperatures and times duringthe post-deposition thermal process.

The behavior of the silicon/platinum/nickel system for temperatures upto 200° C. is as follows:

The platinum (or nickel) film which is first deposited will, duringannealing, start to react, to form a rich metal silicide Pt₂Si or Ni₂Sirespectively When all the platinum or nickel (or another suitable metal)is consumed, the second metal (for example, nickel if platinum is thefirst metal) will then diffuse through the Pt₂Si (or other) film andreaches and reacts with the silicon to form, for example, regions ofNi₂Si (or Pt₂Si). The Ni₂Si and Pt₂Si will convert to the stablesilicide phase NiSi and PtSi respectively. In the meantime, the siliconreacts with the already formed metal-rich silicide for converting thePt₂Si (or Ni₂Si) in the stable mono-silicide phases PtSi (or NiSi). Thisproduces quite complex structures, formed by a mixture of PtSi and NiSi,and characterized by different compounds at the silicon surface.

In addition to the reaction at the silicon surface, some silicide of theexternal metal (e.g. the platinum) is formed at the outer interface withthe inner metal silicide, implying the transport of the silicon with thenickel or platinum. If the anneal continues for a longer time, or at ahigher temperature, a pseudo binary solid solution [Si(NiPt)] is formed.

The inter-diffusion process between the barrier metals and the silicondepends on the polycrystalline structure of the two films; on thethicknesses of the two films; the annealing temperatures and times andthe physical vapor deposition conditions of the platinum and nickelbarrier metals.

To improve a self-stopping silicide process formation, oxygen ispreferably injected into the reaction area during annealing to form asilicon dioxide passivation layer at the outer silicide surface. Thispassivation layer helps to protect the silicide surface during asubsequent unmasked wet etch, for example, with aqua regia at about 54°C. of the unreacted barrier metals, leaving the Schottky silicidebarrier just in the active area of the device.

Note that the oxygen is injected after the silicide is completely formedas desired, to avoid the inhibition or incomplete formation of thedesired silicide thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a silicon wafer having layers or films of platinum andnickel sequentially deposited thereon.

FIG. 2 shows the wafer of FIG. 1 after an anneal process at 200° C. fora given time to cause the formation of a platinum silicide at thesilicon surface.

FIG. 3 shows another silicide process formation of the invention withthe anneal temperature at 300° C. for a given time to cause the Ni topenetrate the fully formed Pt₂Si layer and reaching the silicon surfaceat spaced locations.

FIG. 4 shows another process using an anneal temperature of 400° C. witha NiSi layer reaching the silicon surface and a mixture of Pt₂Si/NiSi atthe top of the wafer.

FIG. 5 shows another process of forming the silicide in which the annealtemperature is raised to 500° C. for a given time in which both NiS andPt₂Si layers are at the silicon surface to create the desired Schottkybarrier height (790 to 800 meV) and (optionally) a SiO₂ layer is grownatop the silicide film to protect the silicon surface since; continuingthe reaction will form a homogeneous SiNiPt film (700 meV).

FIG. 6 shows the step of applying the anode and cathode metals to thetop and bottom respectively of the wafer.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a mono-crystalline silicon wafer 10 having parallel upperand lower surfaces. A film of platinum 11 is first deposited atop wafer10 and a second film 12 of nickel is deposited atop film 11. Films 11and 12 are preferably deposited in a common chamber by sputtering fromrespective targets.

Other metals then platinum and nickel can be used. The device to beformed is a Schottky barrier rectifier of any desired topology (planaror trench).

The thicknesses of the metals used and the annealing temperature andtime are chosen dependent on the desired resulting barrier height andsilicide phases formation (Ni silicide or Pt silicide or NiPt silicide).

In general, both the Pt film and Ni film can vary in thickness between100 Å to 5000 Å to chose a desired barrier height between 650 to 840meV.

In the next process step, shown in FIG. 2, an anneal temperature of 200°C. is applied, causing a reaction at the Si surface to create a Pt₂Sisilicide 13, resulting in a barrier height close to the upper range (820to 840 meV). This reaction continues for the time needed to consume andconvert all of the platinum film 11 to the Pt₂Si layer 13.

In FIG. 3, an anneal temperature of 300° C. is used to cause the Ni filmto infiltrate through the Pt₂Si film 13 and reach the silicon surfaceforming Ni₂Si and giving a barrier height lower than the 200° C.process.

If the anneal temperature is again raised, as shown in FIG. 4 and thenickel now fully infiltrates the Pt₂Si film 13, forming NiSi layer 14.In addition, a Pt₂Si/N₂Si mixture layer 15 is formed atop the Pt₂Silayer 13. The obtained barrier height is in the range of 640 to 840 meV.

If the inter-diffusion process is continued at about 500° C. to completethe desired silicide barrier in FIG. 5 with a barrier height of about790 to 800 meV is obtained and the stable PtSi and NiSi phases areobtained. At the end of this process, oxygen is injected into reactionchamber during ramp-down of the reaction chamber to form the SiO₂ layer20 atop the silicide layer

As next shown in FIG. 6, the surface of the device is cleaned as withdilute HF to remove the layer 20, followed by the deposition of a layerof titanium tungsten 30 and a top contact anode metal 31 and a bottomcathode metal 32. The titanium/tungsten layer acts as a barrier betweenthe Schottky barrier and the anode metal 31.

The wafer is next masked and the metallization and barrier aresequentially etched as usual.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein.

1. The process of forming a Pt/Ni Schottky barrier, comprising the stepsof depositing one of a Pt or Ni film of given thickness atop a siliconwafer surface; then depositing the other of a Pt or Ni film of giventhickness atop the first deposited film and thereafter annealing saidfilms to cause the inter diffusion of Pt and Ni, and the growth of areasof nickel and platinum silicides at the silicon surface to define aSchottky junction barrier in the range of 640 meV to 840 meV.
 2. Theprocess of claim 1, wherein said given thicknesses of said Pt and Nifilms are in the range of 100 Å to 5000 Å, and wherein the barrierheight of said junction depends on the thicknesses chosen for said Niand Pt films and annealing temperature and time.
 3. The process of claim1, wherein said annealing of said films comprises the anneal a selectedtemperature and time.
 4. The process of claim 1, which includes theformation of a passivation coating atop said silicide film to improvethe silicide self aligned process.
 5. The process of claim 3, whereinsaid anneal is in the range of 200° C. to 650° C. to obtain the desiredbarrier height.
 6. The process of claim 5, which includes the formationof a passivation coating atop said silicide film to improve the silicideself aligned process.
 7. The process of claim 3, which further comprisesthe step of forming a SiO₂ passivation layer atop said silicide aftersaid annealing process, to improve the silicide self aligned process. 8.The process of claim 1, which comprises the further step of applying alayer of an anode metal diffusion barrier atop said silicide andapplying an anode contact layer atop said layer of TiW.
 9. The processof claim 7, which further comprises to removal of said SiO₂ passivationlayer to expose the top surface of said silicide and thereafter applyinga layer of TiW atop said silicide and applying an anode contact layeratop said layer of TiW.
 10. The process of forming a Schottky barrier tothe surface of a silicon wafer comprising the steps of depositing afirst barrier forming metal of thickness between 500 Å to 5000 Å atopsaid surface of said silicon wafer; depositing a second barrier formingmetal of thickness between 100 Å to 5000 Å atop said first barrierforming metal; and thereafter annealing said first and second metalfilms to cause their interdiffusion and the growth of areas of silicidesof said first and second metals on said silicon surface to define aSchottky junction barrier of a height dependent on the initialthicknesses chosen for said first and second films and their thermaltreatment.
 11. The process of claim 10, wherein said first and secondfilms are Pt and Ni respectively, and wherein said barrier height is inthe range of 640 meV to 840 meV.
 12. The process of claim 10, whereinsaid annealing of said films is carried out at a preselected temperaturefor a preselected time to produce a predetermined barrier height. 13.The process of claim 10, which includes the formation of a passivationcoating atop said silicide film to improve the self aligned silicideprocess.
 14. The process of claim 12, which includes the formation of apassivation coating atop said silicide film to improve the self alignedsilicide process.
 15. The process of claim 12, wherein said anneal stepsare carried out at a temperature range of 200° C. to 650° C.respectively.
 16. The process of claim 12, which includes the formationof a passivation coating atop said silicide film to improved the selfaligned process.
 17. The process of claim 10, which further comprisesthe step of forming a SiO₂ passivation layer atop said silicide aftersaid anneal process to improve the silicide self aligned process.